Carbon-13 Magnetic Resonance Studies on Charge-Transfer Complexes: Pyridine-Iodine

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Abstract
Carbon‐13 chemical‐shift data on pyridine and its charge‐transfer complex with iodine are presented. The Karplus‐Pople theory of chemical shifts, together with CNDO/2‐SCF MO calculations, is found to lead to good semiquantitative agreement with experiment. It is shown that both bond orders and electron density must be taken into account to obtain agreement with experiment. Carbon‐13 shift measurements, like proton shift measurements, do not enable the amount of charge transfer to be estimated. Under the experimental conditions used, no estimate of the equilibrium constant could be obtained, but the shifts of the carbon atoms in the pure complex were estimated.